In situ reversed deformation of prefatigued aluminum single crystals in the HVEM

Abstract

Utilizing a technique describe earlier by Wall et al., prefatigued aluminum single crystals oriented for single slip, were cyclically deformed in the HVEM operating at 1.5Mev by deforming in mutually perpendicular “X and Y” directions. Deforming in X and Y avoids foil buckling and allows for shear reversal (fatigue). Initial observations are reported here and will aid in the understanding of the micro-mechanisms of cyclic deformation.In situ specimens extracted from prefatigued single crystals (560 cycles, strain amplitude of 1.2 X 10−3at 77K) were oriented in such a manner as to facilitate imaging primary dislocations, b=[0,l,-1], on the primary (111) slip plane. The (111) plane is inclined 25° about the [0,1,-1] direction to increase the projected length of these dislocations for viewing on the TEM screen. The [0,1,-1] direction is also contained in the plane of the specimen foil and is 45° to the tensile axes. The specimens are then tilted to a [1,1,-1] diffracting condition. Nonperforated specimens were prepared by a technique described by Kassner Specimens were then alternately deformed along mutually perpendicular tensile axis in the HVEM.